Field of the Invention
The present invention relates to gas pressure drop installations and, in particular, to City Gate natural gas pressure reduction stations.
Description of the Prior Art
It is generally known and quite common in the industry that natural gas high pipeline pressure has to be reduced at City Gate stations in order to meet the low pressure gas distributing network requirements. Natural gas is a mixture of hydrocarbon used for fuel.
This operation which is performed in so called JT valves cause (due to the Joule-Thomson effect) a natural gas temperature drop. The greater the inlet/outlet gas pressure difference, the more of that drop value. As a result, the natural gas temperature after pressure reduction becomes much less than the City Gate station location's ground temperature. In most situations, the resulting temperatures are less than the critical temperature to freeze H.sub.2 O.
Bearing in mind that both inlet and outlet City Gate pipelines are typically underground, the freezing and ground distortion by heaving will occur in the soil around the downstream pipeline, which leads to the pipeline distraction and eventual failure. A potentially dangerous condition.
To prevent such undesirable developments natural gas at the City Gate stations is constantly heated prior to the pressure reducing JT valve. The typical existing layout comprises a heater and a JT valve connected in series, with the heater inlet connected with the gas pipeline entering the station and the JT valve outlet connected with the gas pipeline leaving the station. The quantity of energy required for the heating process depends on the pressure drop value, flow volume and the inlet gas temperature. This typically varies from station to station and can vary within certain parameters within a single station depending on system feed in relation to downstream product demand.
Nevertheless, the total energy consumption for heating at any given station is always substantial due to the steady flow and the typical volumes of the gas involved.
A vortex tube design as set forth in U.S. Pat. No. 5,327,728 to Tunkel is particularly useful in connection with this invention.